The present invention relates to industrial polyamide yarns and more particularly relates to high tenacity poly(hexamethylene adipamide) yarn having low shrinkage and a process for making such yarns.
A wide variety of high tenacity polyamide yarns are known and are used commercially for a variety of purposes. Many of such polyamide yarns are useful in cords for tires due to high tenacity, i.e., up to but generally not exceeding 10.5 g/d. Such yarns also have tolerable levels of dry heat shrinkage for conversion to tire cords, typically 5-10% at 160.degree. C.
For certain applications such as ropes, industrial fabrics, airbags, and reinforced rubber goods such as hoses and conveyer belts, yarns with shrinkage less than that found in tire yarns are desirable. While some low shrinkage yarns are known, the tenacity of such yarns generally decreases with decreasing shrinkage. The lower tenacity thus requires the usually undesirable use of heavier deniers or the increased number of yarns in the end-use application. Other low shrinkage yarns with high tenacity levels have been made using processes employing treatment steps such as steaming for relatively long periods after drawing but such processes are usually not well-suited for commercial production. In addition, the yarns made by such processes typically have greatly reduced modulus levels and undesirable growth properties.
A heat-stable polyamide yarn with very low shrinkage while at the same time providing high tenacity would be highly desirable for such applications, particularly with a balance of properties including a low shrinkage tension and high modulus. Such yarns would be even more desirable if the yarns were readily manufactured in a commercially-feasible process.